Fluid-blast circuit interrupter with piston assembly and electromagnetic driving means

ABSTRACT

A fluid-blast piston-type circuit interrupter utilizes two stationary accelerating coils and one moving accelerating coil carried by a fluid-driving piston assembly. During the opening operation, the series fault current is inserted serially into the three accelerating coils, and their magnetic attraction and repulsion forces assist the operating mechanism to move the fluid-driving piston assembly, and thereby to drive fluid, such as sulfur-hexafluoride (SF6) gas, through the established arc drawn within an orifice member to effect its extinction.

United States Patent 1111 3,532,5 9

[72] lnventor Russell E. Frink 3,164,703 1/1965 Friedrich et al. 200/l48(.-1)

Pittsburgh, Pa. 3,214,550 10/1965 Easley 200/148(.1) [21] Appl. No. 701,771 3,238,340 3/1966 Lerch 200/l48(.1) [22] Filed In. 30, I968 FOREIGN PATENTS (45] Patented June I, 1971 1,190,079 4/1965 Germany 200/148(. 1)

[73] Assignee Westinghouse Electric Corporation Pittsburgh Pa 1,206,056 12/1965 Germany 200/148( .1

[54] FLUID-BLAST CIRCUIT INTERRUPTER WITH PISTON ASSEMBLY AND ELECTROMAGNETIC DRIVING MEANS 12 Claims, 8 Drawing Figs.

[52] U.S.Cl 200/148, 200/148 [51] Int. Cl ..II01h 33/91 [50] FleldolSearch ZOO/148.1. 148

[56] References Cited UNITED STATES PATENTS 2,913,556 11/1959 Leeds 200/l48(.l)X

Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye At!orneysA. T. Stratton, C. L. McHale and W. R. Crout ABSTRACT: A fluid-blast piston-type circuit interrupter utilizes two stationary accelerating coils and one moving accelerating coil carried by a fluid-driving piston assembly. During the opening operation, the series fault current is inserted serially into the three accelerating coils, and their magnetic attraction and repulsion forces assist the operating mechanism to move the fluid-driving piston assembly, and thereby to drive fluid, such as sulfur-hexafluoride (SF gas, through the established arc drawn within an orifice member to effect its extinction.

PATENTEUJLm H971 3,582,589 summra WITNESSES INVENTOR Russell E. Frink PATENTED JUN H97! 3,582,589

sum 3 OF 3 FLUID-BLAST CIRCUIT INTERRUPTER WITH PISTON ASSEMBLY AND ELECTROMAGNETIC DRIVING MEANS CROSS-REFERENCES TO RELATED APPLICATIONS Reference may be had to U.S. Pat. application filed Sept. 1, 1966, Ser. No. 576,740 by Russell E. Frink and William H. Fischer to illustrate a fluidblast type of circuit interrupter in which accelerating coils are utilized to effect a fluid-driving piston assembly. Additional reference may be had to U.S. Pat. application filed Sept. 1, 1966, Ser. No. 576,616 now US Pat. No. 3,524,958, issued Aug. 18, 1970 to Russell E. Frink, and reference may also be made to US. Pat. application filed Sept. 1,1966, Ser. No. 576,615 now U.S. Pat. No. 3,524,957, issued Aug. 18, 1970 to Russell E. Frink. Also attention may be directed to U.S. Pat. application filed Sept. 1, 1966, Ser. No. 576,739 filed by Russell E. Frink now U.S. Pat. No. 3,524,959, issued Aug. 18, 1970.

An orifice arrangement for such a type of circuit interrupter is illustrated and described in U.S. Pat. application filed Sept. 1, 1966, Ser. No. 576,583 now U.S. Pat. No. 3,551,624, issued Dec. 29, 1970 to William H. Fischer. A floating piston puffer device, pertinent to the general class of circuit breakers herein under discussion, is set forth and described in U.S. Pat. application filed Sept. l, 1966, Ser. No. 576,575 now U.S. Pat. No. 3,551,623, issued Dec. 29, 1970 to William H. Fischer and Gerald Colclaser. A contact and nozzle configuration is set forth in U.S. Pat. application filed Sept. 1, 1966, Ser. No. 576,711 now U.S. Pat. No. 3,529,108, issued Sept. 15, 1970 to Robert M. Roidt. An additional application describing the present class of circuit breakers is set forth and described in U.S. Pat. application filed Feb. 16, I967, Ser. No. 616,544 by Stanislaw Milianowicz U.S. Pat. No. 3,551,626, issued Dec. 29, 1970. Utilizing a three accelerating coil arrangement for a magnetic puffer-type circuit interrupter is set forth and claimed in U.S. Pat. application filed Sept. 29, 1966, Ser. No. 582,925 now U.S. Pat. No. 3,531,608, issued Sept. 29, 1970 to Edmond Bateman. An additional patent application covering a three-magnetic coil arrangement is set forth and described in U.S. Pat. application filed Nov. 21, 1966, Ser. No. 595,889 now U.S. Pat. No. 3,549,842, issued Dec. 22, 1970 to Russell E. Frink and William H. Fischer.

BACKGROUND OF THE INV ENTlON In U.S. Pat. application filed Sept. 1, 1966, Ser. No. 576,740, by Russell E. Frink and William H. Fischer, there is illustrated and described a fluid-blast type of circuit interrupter utilizing a piston assembly and a driver unit attached thereto, which includes two moving accelerating coils and a stationary accelerating coil disposed in the stationary end plate of an operating cylinder. The interrupter disclosed in the aforesaid patent application is housed in a heavy metallic grounded cylinder having a pair of downwardly extending terminal bushings extending through the upper walls of the metallic grounded housing, and serving to support the interrupting unit therein. During the opening operation, a suitable operating mechanism initially causes motion of the piston assembly and the driver unit, which upon initial arc establishment inserts the three accelerating coils serially into the electrical circuit; and their repulsion and attraction forces assist the operating mechanism in effecting fast fluid-driving motion of the piston assembly.

It would be a desirable accomplishment in the construction of a circuit interrupter of the foregoing type to minimize the mass of the moving parts and to generally improve the accelerating forces in assisting the fluid-driving motion of the piston assembly.

SUMMARY OF THE INVENTION According to a preferred embodiment of the present invention, an insulating cylinder is provided, and two stationary accelerating coils are fixed in relation thereto. An internally movable piston assembly, carrying the movable contact structure and a movable accelerating coil, is adapted for reciprocal movement with the contact arrangement so arranged as to insert, during the opening operation, the three accelerating coils into the series electrical circuit. Due to the attractive and repulsive magnetic forces set up by the several coils, the piston assembly is assisted in its opening fluid-driving motion, thereby minimizing the operating requirements imposed upon the adjacent operating mechanism.

This invention relates, generally, to circuit interrupters, and more particularly to circuit interrupters of the fluid-blast type having a piston assembly associated therewith for generating fluid under pressure to be forced into the established arc to effect the extinction thereof.

It is a general object of the present invention to improve upon the fluid-blast circuit interrupter of the aforesaid U.S. Pat. application Ser. No. 576,740 rendering it of reduced size and reducing the mass of the moving parts by utilizing one moving accelerating coil instead of the two moving accelerating coils, as was disclosed in the aforesaid U.S. Pat. application Ser. No. 576,740.

It is another object of the present invention to provide an improved magnetic-puffer type of fluid-blast circuit interrupter of the type utilizing accelerating coils, which are inserted into the series electrical circuit during the opening operation, in which the two stationary accelerating coils are encapsulated within a cast-resin housing, and only a single accelerating coil moves with the piston assembly. As a result, the outer heavy metallic grounded housing, as utilized in the construction of the aforesaid patent application, is eliminated.

Still a further object of the present invention is the provision of an improved fluid-blast circuit interrupter of simple construction, and providing a worthwhile reduction in the moving mass of the moving partsfwhich will permit faster interrupting times and reduce the mechanism requirements.

Still a further object of the present invention is the provision of an improved simplified-type magnetic puffer-type interrupter, in which the use of two stationary accelerating coils, and only a single moving coil moving with the piston assembly, results in a simpler coil connections and a highly effective coiltransfer arrangement.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view in side elevation of a fluid-blast circuit interrupter embodying the principles of the present invention;

FIG. 2 is a longitudinal vertical sectional view taken through the interrupting assembly of FIG. 1, substantially along the line 11-11 of FIG. 3, the contact structure being illustrated in the closed-circuit position;

FIG. 3 is a longitudinal sectional view taken through the interrupting unit of FIG. 2, substantially along the line 111-111 of FIG. 2, again the contact structure being illustrated in the closed-circuit position;

FIG. 4 is a view similar to that of FIG. 2, but illustrating the disposition of the several parts during the opening operation, when arcing occurs;

FIG. 5 is a horizontal sectional view taken substantially along the line VV of FIG. 2;

FIG. 6 is a vertical sectional view taken substantially along the line VI-VI of FIG. 2;

FIG. 7 illustrates, in perspective, the general arrangement of the two stationary accelerating coils and the coil connections therefore; and,

FIG. 8 is a diagrammatic view of the electrical connections for the circuit interrupter.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, and more particularly to FIG. 1 thereof, the reference numeral 1 generally designates a magnetic-type fluid-blast circuit interrupter. The circuit interrupter 1 has end terminal pad portions 2, 3, to which line connections L,, L are attached. A composite insulating inter rupter casing 4 is provided.

Supporting insulators 5,6 insulatingly support the interrupting assembly laterally an adequate voltage-withstanding distance from a grounded supporting framework 7, comprising structural steel angle members 8, 9, and vertical braces 12, 13. A mechanism 14 is provided to effect opening and closing rotative movement of an external operating crank 15, as more fully described hereinafter.

Again referring to the drawings, and more particularly to FIGS. 2 and 3 thereof, it will be noted that the interrupting unit is housed within an insulating composite cylinder 4. The stationary magnetic coils 17, 18 are made from edge-wound copper strap, for example, to which tapped terminal blocks are brazed, or otherwise affixed. The coils 17, 18 after winding and brazing the terminals, are taped over the individual turns with mica tape, for example; and each entire coil 17 or 18 is then compressed and taped, as a unit, with Dacron tape, for example, and the coil impregnated with epoxy resin. The two coils 17, 18 are then positioned over the tube 4a and held in place with wedges (not shown) of the same material, as is used in the outer tube 4b. Terminals are then bolted to the coil-terminal blocks with the tabs of connectors extending into the inner volume or interior of the operating cylinder 4 through slits 23 provided in the tube wall 4a. Tight fitting, lubricated mandrels (not shown) are then placed inside the tube 4a from either end, and meeting at the position of the connectors. A split mold is then placed around this assembly, and the housing 4 is cast by conventional epoxy casting techniques.

Attached to both ends of the cylindrical housing 4 by bolts 24, threaded into metal inserts 25 are the terminal members, or end casting portions 26, 27. These terminal members ex tend a short distance into the cylindrical housing, and are sealed by O-rings 28. Attached to terminal member 26 by sealed bolts 29 is the Ushaped stationary conductor 31. Brazed to the open end of the U member 31 are sections 33 of extruded copper, for example, which act as pivots for reverseloop fingers 34. The fingers 34 are biased inwardly by springs 35 (FIG. 3) and are restrained by clips 36. Attached to the extruded sections 33 by bolts 37 (FIG. 3) is a stationary disc 39 of SF -resistant insulating material, which fits closely to the inside diameter of the cylindrical tube 4, and is sealed by the O- ring 40. Moving longitudinally within the cylinder is a movable piston assembly 43, which is operated by the two insulating links 44, which are attached by pins 45 to clevises 46, which are a part of the movable piston assembly 43. The opposite or lower ends of links 44 are attached by pins 47 to the lever 48, which is pinned to shaft 49 by pins 50. Operating shaft 49 extends through terminal member casting 27, and has the operating lever welded to its external end. Gas leakage is prevented by a seal 52.

The movable piston assembly 43 is built on a molded disc 54 of insulating material, which fits closely within the internal diameter of tube 4, gas leakage being kept low by the piston ring 55. Threaded into the piston are guide rods 56, 57, which are secured into position by jam nuts 58. The movable piston accelerating coil 60 has its terminals 61, 62 maintained in contact with the movable guide rods 56,57 by metallic spacers 63 and nuts 64. The tubular moving main contact member 66 has brazed to it a metallic spider 67, which is attached to the movable piston 43 by bolts 68 FIG. 6. Nested within a cavity 69, provided in the movable piston member 54 and resting upon spider 67, is a stack of cooling screens 70. A retaining member 71, which has suitable apertures 71a provided therein, compresses the stack of screens 70 and is held into position by the insulating movable gas-flow guide tube 72. The entire assembly is held together by the insulating cover plate 74, which is secured by spider bolts 68 and clevis bolts 77. The main movable contact tube 66a extends through an opening 78 (FIG. 2) in the stationary end plate 39, gas leakage being deterred by a sealing ring 8]. Threaded to the main movable contact tube 66a is a movable contact member 83, which is elongated in one direction to make contact with the stationary contact fingers 34 when the breaker 1 is in the closed-circuit position, as illustrated in FIGS. 2 and 3 of the drawings. Concentrically located with respect to the movable main contact tube 66 is the movable arcing contact tube 85, which is positioned at its lower end by an insulator 87 and at its upper end by an insulating strip 88, which is bolted to contact member 83 by bolts (not shown). The insulating strip 88 is also attached to the guide rods 56, 57 by jam nuts 90. The movable arcing contact tube a is connected to guide rod 56 by conducting strap 92. The guide rod 57 passes through a sliding ball contact 94 (FIG. 2), which is set forth and claimed in U.S. Pat. No. 3,301,986 issued to Russell E. Frink, Jan. 31, 1967, and assigned to the assignee of the instant application. The ball contact 94 is electrically connected to the terminal strap 95 (FIG. 2) of the stationary accelerating coil 17. Referring to FIG. 5, the terminal strap 96 of stationary accelerating coil 17 is bolted, as at 97, to an extension 98 of one of the extruded sections 33.

With reference to FIGS. 2 and 3 of the drawings, it will be noted that the stationary contact member 100 is clamped to a stationary conducting casting 101, which is bolted to the end casting 27 by bolts 102. The external circuit connections L,, L to the interrupter are through the terminal pads 2, 3 and the interrupter is supported by the grounded metallic framework 7 (FIG. I), which is secured to the supporting insulators, as previously described.

OPENING OPERATION OF THE INTERRUPTER With the circuit interrupter closed as in FIGS. 1 and 2, the current path therethrough is through line connection L,, terminal pad 2, end plate 26, stationary contact structure 34, movable contact structure 83, movable main contact tube 66a, movable contact 66, stationary contact 100 through stationary main contact tube 100a, through conducting support casting 101 and end casting portion 27 and terminal pad 3 to the lower line terminal L When the mechanism 14 operates to move the piston assembly 43 upwardly, as viewed in FIGS. 2 and 3, arcs 111, 113 are drawn between the separable contact structure 34, 83 and also between the separable contact structure 66, 100, with the SF gas 115 being compressed by the upwardly moving piston assembly 43 within the space 117. The gas flows downwardly, through the are 113, established between movable and stationary main contacts 66, 100 and causes the are 113 to transfer to movable arcing contact 85, and stationary arcing contact 100b. This new are position 113a is shown in FIG. 4. The current path is now line connection L end casting 26, stationary contact 33, terminal strap 96, stationary accelerating coil 18 (FIG. 7), coil connection 119, stationary accelerating coil 17, coil terminal 95, ball contact 94, conducting guiderod 57, coil connection 62, movable accelerating coil 60, movable coil terminal 61, conducting guide rod 56, conducting strap 92, movable arcing tube 85a, movable arcing contact 85, the are 113 (FIG. 4), the interior of stationary contact nozzle 100b, conducting support casting 101 to end conducting plate 27 and lower line terminal con nection L It will be noted that the short circuit current now flows through the three accelerating coils 18, 17 and 60 in series, and the movable coil 60 is repelled by coil 18 and attracted by coil 17 giving a powerful assist to the operating mechanism 14 in moving the piston assembly 43 upwardly in its fluid-driving motion, thereby driving gas through the transferred arc 113a (FIG. 4) to interrupt it, the gases exhausting through both tubular contact structures.

From the foregoing description, it will be apparent, that there has been provided a compact low-cost circuit interrupter 1 of highly effective operation, and utilizing a minimum amount of mass in the moving parts. Although the construc tion is particularly suitable for the lower voltage ratings, as, for example 23 KV up through 34.5 KV, it will be apparent that certain of the broader features of the invention may be applied to circuit interruptcrs of the magnetic puffer-type, for the higher voltage ratings. A very important feature of the invention is the utilization of the fault current energy for assisting the operation mechanism 14 in moving the piston assembly 43 in a fluid-driving direction, and thereby ensuring an adequate gas flow during heavy arcing conditions by the increased magnetic effect exerted by the three accelerating coils.

FIG. 8 diagrammatically illustrates, generally, the moving contact structure and coil connections for the circuit interrupter.

During the closing operation, the mechanism 14 functions to move the moving contact assembly 66 and the piston assembly 43 downwardly to cause contact reclosure to the closed circuit position illustrated in FIGS. 2 and 3 of the drawings.

Although there has been illustrated and described a specific structure it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

lclaim:

l. A fluid-blast piston-type circuit interrupter including, in combination:

a. means defining a stationary insulating operating cylinder,

b. a pair of stationary accelerating coils spaced axially along said stationary operating cylinder and supported thereby,

c. a fluid-driving movable piston member reciprocally movable within said operating cylinder and carrying therewith a third movable accelerating coil,

d. a relatively stationary contact structure,

e. relatively movable contact structure including a main movable contact and a movable arcing contact insulated therefrom,

-f. means electrically connecting the three accelerating coils in series between a terminal of the interrupter and said movable arcing contact,

g. means for initially establishing a main current are between the main movable contact and said relatively stationary contact structure,

h. means for transferring one terminal of said are to the movable arcing contact to thereby insert the three accelerating coils serially into the electrical circuit,

i. fluid-directing means for directing fluid compressed by the piston action into the transferred arc to effect extinction thereof and thereby effect circuit interruption,

j. and the location of said pair of stationary accelerating coils being such relevant to the moving accelerating coil that one stationary accelerating coil magnetically repels the moving accelerating coil and the other stationary accelerating coil magnetically attracts said movable accelerating coil.

2. The fluid-blast circuit interrupter of claim 1, wherein the fluid-directing means comprises an insulating nozzle movable with the movable piston member and encompassing at least a portion of the stationary contact structure.

3. The fluid-blast circuit interrupter of claim I, wherein the relatively movable contact structure comprises a pair of concentrically arranged movable conducting tubes.

4. The fluid-blast circuit interrupter of claim 3, wherein the tubes pass through an aperture in a fixed closure member fixedly disposed within the stationary operating cylinder.

5. The fluid-blast circuit interrupter of claim 4, wherein a pair of conducting guide rods transmit current from the moving accelerating coil to the movable arcing contact and to one coil terminal ofa fixed accelerating coil.

6. The fluid-blast circuit interrupter of claim I, wherein the movable and stationary contacts are vented for exhausting the gases in opposite directions during circuit interruption.

7. The combination according to claim 1, wherein an operating mechanism is providedto give an initial thrust to the movable piston member.

8. The combination according to claim 1, wherein the transferring means includes a blast of fluid provided by the initial movement ofthc movable piston.

9. The combination according to claim I, wherein the relatively stationary contact structure and the movable contact structure are vented.

10. A fluid-blast piston-type circuit interrupter including, in combination:

a. means defining a stationary insulating operating cylinder,

b. a pair of stationary driving coils spaced longitudinally along said stationary operating cylinder adjacent first and second ends thereof and supported thereby,

. a stationary main contact disposed adjacent the first end of said operating cylinder,

d. a stationary auxiliary contact disposed adjacent the second end of said operating cylinder,

a movable contact structure and piston assembly mechanically connected together and arranged to move as a unit,

. operating means connected to said piston assembly and functioning to effect opening and closing movement thereof reciprocally within said stationary operating cylinder,

. said movable contact structure comprising a movable main contact and a movable auxiliary contact electrically connected together and respectively engaging and disen gaging the stationary main contact and the stationary auxiliary contact,

. said movable assembly further comprising a third driving coil and a movable arcing contact,

. means electrically connecting the three driving coils in series between said stationary auxiliary contact and said movable arcing contact, 7

. means effecting transfer of one terminal of the main current arc to said movable arcing contact to thereby insert the three driving coils serially into the electrical circuit during the opening operation,

k. and the location of said pair of stationary driving coils being such relative to the third driving coil that one stationary driving coil magnetically, repels the moving driving coil and the other stationary driving coil magnetically attracts said moving driving coil.

11. The fluid-blast circuit interrupter of claim 10, wherein the movable and stationary contacts are tubular and vented for exhausting the gases in opposite directions during circuit interruption.

12. The fluid-blast circuit interrupter of claim 10, wherein the transfer means comprises an insulating fluid-directing nozzle carried by said piston assembly to direct gas flow into the are. 

1. A fluid-blast piston-type circuit interrupter including, in combination: a. means defining a stationary insulating operating cylinder, b. a pair of stationary accelerating coils spaced axially along said stationary operating cylinder and supported thereby, c. a fluid-driving movable piston member reciprocally movable within said operating cylinder and carrying therewith a third movable accelerating coil, d. a relatively stationary contact structure, e. relatively movable contact structure including a main movable contact and a movable arcing contact insulated therefrom, f. mEans electrically connecting the three accelerating coils in series between a terminal of the interrupter and said movable arcing contact, g. means for initially establishing a main current arc between the main movable contact and said relatively stationary contact structure, h. means for transferring one terminal of said arc to the movable arcing contact to thereby insert the three accelerating coils serially into the electrical circuit, i. fluid-directing means for directing fluid compressed by the piston action into the transferred arc to effect extinction thereof and thereby effect circuit interruption, j. and the location of said pair of stationary accelerating coils being such relevant to the moving accelerating coil that one stationary accelerating coil magnetically repels the moving accelerating coil and the other stationary accelerating coil magnetically attracts said movable accelerating coil.
 2. The fluid-blast circuit interrupter of claim 1, wherein the fluid-directing means comprises an insulating nozzle movable with the movable piston member and encompassing at least a portion of the stationary contact structure.
 3. The fluid-blast circuit interrupter of claim 1, wherein the relatively movable contact structure comprises a pair of concentrically arranged movable conducting tubes.
 4. The fluid-blast circuit interrupter of claim 3, wherein the tubes pass through an aperture in a fixed closure member fixedly disposed within the stationary operating cylinder.
 5. The fluid-blast circuit interrupter of claim 4, wherein a pair of conducting guide rods transmit current from the moving accelerating coil to the movable arcing contact and to one coil terminal of a fixed accelerating coil.
 6. The fluid-blast circuit interrupter of claim 1, wherein the movable and stationary contacts are vented for exhausting the gases in opposite directions during circuit interruption.
 7. The combination according to claim 1, wherein an operating mechanism is provided to give an initial thrust to the movable piston member.
 8. The combination according to claim 1, wherein the transferring means includes a blast of fluid provided by the initial movement of the movable piston.
 9. The combination according to claim 1, wherein the relatively stationary contact structure and the movable contact structure are vented.
 10. A fluid-blast piston-type circuit interrupter including, in combination: a. means defining a stationary insulating operating cylinder, b. a pair of stationary driving coils spaced longitudinally along said stationary operating cylinder adjacent first and second ends thereof and supported thereby, c. a stationary main contact disposed adjacent the first end of said operating cylinder, d. a stationary auxiliary contact disposed adjacent the second end of said operating cylinder, e. a movable contact structure and piston assembly mechanically connected together and arranged to move as a unit, f. operating means connected to said piston assembly and functioning to effect opening and closing movement thereof reciprocally within said stationary operating cylinder, g. said movable contact structure comprising a movable main contact and a movable auxiliary contact electrically connected together and respectively engaging and disengaging the stationary main contact and the stationary auxiliary contact, h. said movable assembly further comprising a third driving coil and a movable arcing contact, i. means electrically connecting the three driving coils in series between said stationary auxiliary contact and said movable arcing contact, j. means effecting transfer of one terminal of the main current arc to said movable arcing contact to thereby insert the three driving coils serially into the electrical circuit during the opening operation, k. and the location of said pair of stationary driving coils being such relative to the third driving coil that one stationary driving coil magneTically, repels the moving driving coil and the other stationary driving coil magnetically attracts said moving driving coil.
 11. The fluid-blast circuit interrupter of claim 10, wherein the movable and stationary contacts are tubular and vented for exhausting the gases in opposite directions during circuit interruption.
 12. The fluid-blast circuit interrupter of claim 10, wherein the transfer means comprises an insulating fluid-directing nozzle carried by said piston assembly to direct gas flow into the arc. 